The present invention relates to a polishing apparatus for polishing a substrate, such as a semiconductor wafer. Specifically, the present invention relates to a polishing apparatus including a novel dresser device. The dresser device is used for regeneration (dressing or conditioning) of a polishing surface of a polishing pad or a polishing plate comprising abrasive particles.
The present invention also relates to a polishing apparatus for polishing a workpiece to be polished and in more specific, to a polishing apparatus for polishing a workpiece to be polished, such as a semiconductor wafer and so on, having a thin film deposited on a surface thereof so as to have a flat and mirror finished surface.
A conventional polishing apparatus of the above-mentioned type is shown in FIG. 1. In FIG. 1, the polishing apparatus comprises a turntable (polishing table) 1 having a polishing pad 2 covering an upper surface thereof and a substrate holder 3 for holding a substrate (not shown) to be polished, such as a semiconductor wafer. A substrate is held on a lower side of the substrate holder 3 and is pressed against a polishing surface of the polishing pad 2 on the turntable 1. While pressing the substrate against the polishing surface, an abrasive liquid is supplied onto the polishing surface, and relative movement between the polishing pad 2 and the substrate is conducted by rotating the turntable 1 in a direction indicated by an arrow A and rotating the substrate holder 3 in a direction indicated by an arrow B. Thus, the substrate is polished to a flat and mirror-finished surface. It should be noted that a polishing plate comprising abrasive particles may be used, instead of the polishing pad 2.
In this apparatus, the polishing surface of the polishing pad 2 becomes clogged after polishing of a plurality of substrates, to thereby lower an efficiency of polishing. Therefore, when a predetermined number of substrates have been polished or the efficiency of polishing has been lowered due to clogging, the polishing surface is scraped for dressing, by means of a dresser 4.
The dresser 4 comprises a dresser tool 5 and a dresser shaft 6 for supporting the dresser tool 5. The dresser shaft 6 is adapted to be rotated by means of a rotary mechanism (not shown) in a direction indicated by an arrow C. The dresser tool 5 is adapted to be pressed against the polishing pad 2 by means of an air cylinder 7 and the dresser shaft 6. An annular projection 5a is formed on a lower surface of the dresser tool 5. The annular projection 5a is formed from a member (such as a diamond pellet) containing diamond particles or a hard material such as a ceramic material. A relative movement between the dresser tool 5 and the polishing pad 2 is conducted by rotating the dresser shaft 6 and the turntable 1, to thereby scrape the polishing surface of the polishing pad 2 for dressing.
For effecting dressing of the polishing surface of the polishing pad 2, air is supplied through the controller 8 to the air cylinder 7, so as to press the dresser tool 5 against the polishing pad 2 under a predetermined pressure. Therefore, the minimum pressure applied to the polishing pad 2 (the pressure when no air is supplied through the controller 8 to the air cylinder 7) is equal to the total of the weight of the dresser tool 5 and the weight of the dresser shaft 6.
During dressing, as shown in FIG. 2, the rate (mm/hr) of scraping of the polishing pad 2 is proportional to the pressure applied to the polishing pad 2. Generally, the total of the weight of the dresser tool 5 and the weight of the dresser shaft 6 is about 10 kg, so that it is impossible to reduce the pressure applied to the polishing pad to less than 100 N (Newton). Therefore, the polishing pad 2 is scraped at a high rate, leading to a rapid wear of the polishing pad 2.
In recent years, as an integration level of semiconductor device progresses, a wiring pattern of circuit has become more micro-fabricated and thereby a space between wirings is getting much narrowed. Especially, in a photo lithography with a line width equal to or less than 0.5 μm, a shallow focal depth thereof requires a high level of flatness in a surface of the semiconductor wafer on which a stepper forms an image. One of known means available for flattening the surface of such semiconductor wafer is a polishing apparatus that can provide the chemical and mechanical polishing (CMP).
This type of polishing apparatus typically comprises, as shown in FIG. 19, a polishing table 302 with a polishing surface formed by a polishing cloth (a polishing pad) affixed thereon and a top ring 304 for retaining a substrate W such as a semiconductor wafer or the like, which has been prepared as a workpiece to be polished, such that a surface of the substrate W to be polished may face to the polishing table 302. To perform a polishing operation of the semiconductor wafer W by using such a polishing apparatus, the semiconductor wafer W may be pressed against the polishing cloth 300 of the polishing table 302 under a predetermined pressure applied by the top ring 304 while driving the polishing table 302 and the top ring 304 to rotate about their own axes respectively and supplying an abrasive liquid from an abrasive liquid supply nozzle 306 arranged above the polishing table 302.
As for an abrasive liquid supplied from the abrasive liquid supply nozzle 306, for example, a suspension containing abrasive grains composed of fine particles of silica or the likes suspended in an alkaline solution may be used, so that the chemical and mechanical polishing achieved by a combined effect of the chemical polishing action by the alkali with the mechanical polishing action by the abrasive grains may be provided to polish the semiconductor wafer W to have a flat and mirror finished surface. Recently, instead of the polishing cloth, such a bonded abrasive may be used that is composed of the abrasive grains like cerium dioxide (CeO2) or the likes which have been bonded by using a binder.
When such a polishing apparatus is used to carry out the polishing process continuously for a certain time period, the polishing ability of the polishing surface of the polishing cloth 300 may be deteriorated, and so a dresser 308 having a dressing element 310 disposed on an under surface thereof is provided in order to recover this polishing ability, which applies a dressing treatment to the polishing cloth 300 during such an occasion as changing semiconductor wafers W to be polished. In this dressing process, the dressing elements 310 of the dresser 308 are pressed against the polishing cloth 300 of the polishing table 302 while driving them to rotate about their own axes respectively, so that the abrasive liquid and the ground-off chips adherent to the polishing surface may be removed and at the same time, the polishing surface can be flattened and dressed to regenerate the polishing surface. This dressing is also referred to as conditioning.
When the bonded abrasive is used as the polishing surface for example, because the bonded abrasive is not so flexible as the polishing cloth, the surface of the bonded abrasive would not be easily deformed so as to follow a change in the contour of the contact surface of the dressing element 310 of the dresser 308. Consequently, the dressing element 310 cannot come into full-face-contact with the polishing surface of the bonded abrasive but only a part of the dressing element 310 can come into contact therewith. Especially, in case where the bottom surface of the dressing element 310 has a larger area, a contact area of the dressing element 310 with the polishing surface may be significantly small. In such a case, a uniform dressing would not be applied to the polishing surface, which could inversely affect and give some damages to a uniformity of the semiconductor wafer W across a surface thereof and a stability in polishing operation.
Further, in such a case, a larger load tends to be applied locally to a specific region on the polishing surface of the polishing cloth 300 or the bonded abrasive where the dressing element 310 is in contact therewith, which could cause a large-sized defect on the polishing surface and also shorten the lifetime of the dressing element 310. The physical phenomenon pointed above may occur in dependence on a degree of flatness of the dressing element 310 as well as a precision in assembling and installation of the dressing element 310, and it may be remarkably emphasized especially in case of a smaller load applied to the dresser 308.